1. Field of the Invention
The present invention relates to a shank flange for use in an acoustic piano and the like for supporting a hammer which makes a pivotal movement in response to depression on an associated key of the piano.
2. Description of the Prior Art
FIG. 1 illustrates a hammer 20 and a shank flange 31 provided for each key 2 (see FIG. 3) in a grand piano. The hammer 30 comprises a hammer shank 32, a hammer head 33, and the like. The hammer shank 32 is formed of a wood material in an elongated rod shape, with the hammer head 33 disposed at a rear end thereof. The hammer shank 32 has two furcate arms 32a branching off in two at a front end thereof. The arms 32a extend forward in parallel with each other.
Conventionally, the shank flange 31 is generally made of a wood material. This is because the wood material has the advantage of being readily available, highly workable, and highly rigid though being light in weight. The shank flange 31 is fixed to a hammer shank rail 23 through a flange screw 38 (see FIG. 3). The shank flange 31 is formed with a protuberance 31b of a predetermined width which protrudes backward from a rear end thereof. The protuberance 31b is inserted between the two arms 32a. A pin 35 extends through the arms 32a and protuberance 31b, such that the hammer shank 32 is supported by the shank flange 31 through the pin 35 for pivotal movements about the horizontal axis.
The protuberance 31b of the shank flange 31 has both side surfaces formed in parallel with each other and opposing each other with a slight clearance between each side surface and the inner surface of the associated arm 32a of the hammer shank 32. A cylindrical shank roller 37 is attached at a front end of the bottom surface of the hammer shank 32. The hammer shank 32 is carried by a repetition lever 4 (see FIG. 3) of an action 1 through the shank roller 37.
In the foregoing structure, as the key 2 is depressed, the hammer shank 32 is pushed up by a jack 5 of the action 1 through the shank roller 37 to induce a pivotal movement of the hammer 30, causing the hammer head 33 to strike a string S, thereby generating associated sound from the piano (see FIG. 3). During the pivotal movement of the hammer 30, the hammer shank 32 is guided by the arms 32a and protuberance 31b, thus permitting the hammer 30 to make the pivotal movement without lateral oscillations.
Another known conventional shank flange is disclosed, for example, in Laid-open Japanese Utility Model Application No. 62-146194. This shank flange is designed to serve as a bat flange for pivotably supporting a bat of a hammer in an upright piano. The bat flange is made of an ABS resin instead of a wood material.
As mentioned above, the wood material has been conventionally used for the shank flange 31 in general because of the light weight and high rigidity provided by the wood material. Particularly, since the shank flange 31 functions to support the hammer 30, the shank flange 31 is required to be highly rigid such that the hammer 30 can make a stable pivotal movement even if the key 2 receives a hard blow. On the other hand, however, the wood material, which is a natural material, has the disadvantages of varying in rigidity and weight due to its poor homogeneity as well as of being susceptible to deformation such as bowing and twisting possibly caused by a residual stress. Also, since the wood material largely varies in dimensions depending on the humidity, the width of the protuberance 31b relatively largely expands or shrinks in response to the varying humidity when it is used for the shank flange 31 illustrated in FIG. 1. Particularly, in the shank flange 31, the clearances between the protuberance 31b and the arms 32a of the hammer shank 32 are originally set narrow, the expansion and shrinkage of the protuberance 31b due to the varying humidity cause the hammer shank 32 to be too loose or too tight with respect to the shank flange 31, resulting in a possible failure of a stable pivoting speed of the hammer 30 in response to a particular strength of depression on the key 2.
When the shank flange 31 is made of an ABS resin as disclosed in Laid-open Japanese Utility Model Application No. 62-146194, the resulting shank flange 31, though free from the aforementioned disadvantages involved in the wood material, tends to have an insufficient rigidity, as compared with the wood material, possibly failing to assure a satisfactorily stable action of the hammer 30 when the key 2 receives a hard blow. Also, the ABS resin, which has a larger specific gravity than the wood material, will cause an increase in the weight of the overall piano. In addition, since the ABS resin has a high electric insulating property, static electricity can be generated by friction between the hammer shank 32 and the shank flange 31, associated with the action of the hammer 30. The static electricity thus generated has no way to flow and tends to charge on the shank flange 31. The charge on the shank flange 31 would cause dust and the like to stick on the shank flange 31, possibly resulting in a defective action of the hammer 30, an aesthetically damaged appearance, and the like.